This present invention relates to a lead assembly including an electrode which is adapted for connecting a living organ to an electrical device. In the preferred embodiment shown herein the subject invention is adaptable for a pacing and sensing lead assembly which is transvenously implantable for electrically connecting a heart pacemaker device or generator with cardiac tissue.
In pacemaker technology and related arts, a body-implanted, intravascular lead assembly is oftentimes used which comprises an electrical conductor in a catheter-like construction, adapted at its proximal end to be suitably connected to a source of electrical energy, sometimes referred to as a generator or pacemaker. The assembly further includes an electrode means at the distal end of the conductor which is adapted to be secured to body tissue. With pacemakers, an intravenous transplantation method may be utilized to install the lead assembly. With this method, the electrode means is pushed into the heart through a blood vessel.
In the typical lead assembly for use in the above-purposes, the lead assembly of an electrical conductor and electrode means affixed to the end of the conductor is adapted to be firmly lodged in and permanently secured to and removable when desired from tissue inside the body at a desired location. The conductor and the portion of the electrode means affixed to the conductor are sealed from body fluids and tissue by a material substantially inert to body fluids and tissue. Means are provided for permitting the lead and electrode means to be inserted into and guided through a body vessel to a position inside the body without causing injury to the body vessel and for permitting the electrode means to be firmly lodged in and permanently secured to body tissue. The electrode of the lead assembly may be firmly anchored to tissue which is heart muscle by a helix of suitable electrode material within the sheath of the lead assembly, the electrode being rotated in corkscrew-like fashion for screwing the electrode into the tissue by rotating the conductor and thus rotating the helix of the electrode for affixation.
Lead assemblies of this type are disclosed in U.S. Pat. Nos. 4,106,512 and 4,886,074 to Bisping, incorporated by reference herein in their entirety, which have a flexible helical conductor whose end has a helix-like electrode. Commercial versions of such leads are adapted to make use of a rotational force exerted from the proximal end to cause rotational movement of the conductor such that it can cause the helix electrode to be either extracted from or screwed into the tissue against which it is brought to bear. With this type of lead assembly where the forces must be exerted from the proximal end, difficulties may be encountered in that, due to forces along the electrical conductor and the insulating sheath or tube carrying it, friction caused thereby may result in undue effort at the proximal end and loss of a substantial amount of that effort over the length of the conductor due to torsional absorbance, all of which is not particularly desirable.
Various sheath or tubing materials have been used to carry the elongated conductor such as polyurethanes or fluoropolymers. However, these materials lack the flexibility of silicone. Unfortunately, silicone possesses a tacky surface and is unable to provide low coil rotation resistance.
It is a primary purpose of this invention to lower and thereby improve the coil rotation resistance and slip characteristics of tacky silicone tubing to the point where it is more desirable for use in such devices than the other tubing materials. Long term benefits also accrue in that less cold flow of the silicone will occur over time, as during shelf life, tending to decrease likelihood of inner coil sticking to the tube.